CTLA4 and small cell lung carcinoma: Multiple trials have substantiated the survival benefits of blocking the cytotoxic T-lymphocyte-associated protein 4 (CTLA-4), programmed death 1 (PD-1), and programmed death ligand 1 (PD-L1) axis, either in conjunction with chemotherapy or as maintenance therapy, for ES-SCLC patients [19–21].